phone memory required to install apk? - memory structure of Android

I want to know that in my manifest.xml file I have put permission to install application on sdcard only. Because apk contains a very large zip file inside assets folder. (First I put zip in sdcard and during installation my program was finding that zip but client wants it inside apk only) it was running fine when the size of zip was upto 15 or 20 MB. But when I tried with the zip of 60 MB (inside apk only), I got the exception while installation,

and memory card has 6GB of free memory. Then why am I getting this exception ?!?